In conventional endoscope apparatuses, in order to generate a normal image, image pickup is performed by emitting white light using solid-state image sensing devices that have color filters having wideband color transmission characteristics, or by emitting surface-sequential wideband illumination light of R, G, B or the like using monochrome solid-state image sensing devices.
On the other hand, in body tissues, light absorption characteristics and spectral characteristics vary depending on wavelengths of emitted light. For example, in Japanese Unexamined Patent Application Publication No. 2002-95635, as a first known art, there is disclosed an endoscope apparatus for narrowband observation that emits narrowband RGB surface-sequential light in a visible band on a body tissue, and obtains tissue information at a desired depth of the body tissue.
Moreover, in Japanese Unexamined Patent Application Publication No. 2003-93336, as a second known art, there is disclosed an electronic endoscope that performs signal processing with respect to an image signal for generating a normal image that is obtained by illumination light of a visible band to generate a discrete spectral image (or, narrowband image) and obtain narrowband image information with respect to a body tissue.
In the second known art, there is disclosed an electronic endoscope provided with R, G, B filters for separating colors in a wide band in a visible band so that normal images are generated.
In the first known art, an optical narrowband bandpass filter is employed. However, in the apparatus according to the second known art, without using the optical narrowband bandpass filter, a narrowband image signal is generated by performing signal processing.
Moreover, as a third known art, in Japanese Unexamined Patent Application Publication No. 4-357926, there is disclosed an endoscope apparatus that can obtain a normal image in a visible band and an infrared or ultraviolet image other than the visible band.
In the third known art, there is disclosed the electric endoscope that has color filters of cyan (Cy), G, yellow (Ye) that separate colors in a wide band in the visible band, and the color filters are set to have characteristics to further transmit infrared light.
Moreover, as a forth known art, in FIG. 14 in an endoscope apparatus in Japanese Unexamined Patent Application Publication No. 6-315477, there is disclosed an electronic endoscope that forms images on a CCD which splits incident light using a beam splitter and is provided with a color filter for normal images, and on a CCD which is provided with narrowband filters for special light (more specifically, for acquisition of blood information).
In the first known art, it is necessary to change the illumination light depending on whether a normal image or a narrowband image is to be obtained.
On the other hand, in the second known art, it is not necessary to change the illumination light, and the illumination light of the visible band is constantly emitted.
Based on the signal captured under the illumination light, estimation processing of the narrowband image signal is electrically performed. Accordingly, the processing is apt to be effected by a reflection characteristic or the like of the observation subject. Accordingly, as compared with the first known art, it is difficult to generate narrowband image signals excellent in precision.
That is, in the second known art, it is difficult to generate reliable narrowband images.
In the third known art, it is possible to obtain the infrared or ultraviolet image, however, it is not possible to generate narrowband image signals in illumination conditions to obtain normal images.
In the forth known art, it is possible to obtain normal images and narrowband images under illumination of white light. However, two CCDs, for the normal images and for the narrowband images, are disposed in a distal end portion of an insertion portion of the electronic endoscope. Accordingly, the insertion portion is wide, and it is disadvantageous.
The present invention has been made in view of the above, and an object of the present invention is to provide an endoscope and an endoscope apparatus capable of narrowing a diameter of an insertion portion and capable of generating a normal image and a narrowband image using illumination of illumination light in a visible band.